Sagebrush Coordinate Self-Defense Against Bugs

When an
insect munches on a sagebrush leaf, the wound releases volatile compounds. They
waft into the air and incite other leaves to mount a chemical defense in
preparation for attack. (Internal signaling, via the stems, doesn’t seem to
communicate that particular message in sagebrushes.)

The leaves of nearby
sagebrush plants “overhear” and respond defensively, as do those of the damaged
individual itself. But a plant’s reaction is stronger to its own chemical
warnings than to those issued by strangers, Richard Karban of the University of California,
Davis, and Kaori Shiojiri of Kyoto University
in Japan
have just discovered.

The two biologists measured how much herbivory sagebrushes suffered when they spent a
summer next to either a wounded clone of themselves or a wounded individual
that wasn’t related. Insect damage was 42 percent lower in plants that had
received airborne messages from their clones.

Karban and Shiojiri conclude that the volatile cue has a chemical signature to which the
sender is most sensitive. That signature may be determined genetically, so
close relatives could also be more responsive to it. The biologists point out
that the ability to distinguish self and family from others is an evolutionary
prerequisite to favoring kin in competition—a further step so far observed only
in plants whose roots are touching.